1. Field of the Invention
This invention relates generally to the field of weight distribution devices.
More particularly, this invention relates to weight distribution devices for use in combination with vehicles.
In a further and more specific aspect, the instant invention relates to a trailing axle assembly for use with vehicles of a type operative for carrying a load.
2. Prior Art
For many years, trucks have been used to transport loads. Dump trucks, refuse trucks and many other types of trucks generally include a cargo body carried by a truck frame. A tailgate may be inclined against the rear end of the cargo body. The tailgate may be movable between a closed and open position. In the closed position, the tailgate and the cargo body define a chamber within which a load may be placed. In the open position, the tailgate opens at the rear end of the truck to allow removal of the load from the cargo body. For dump trucks, the front of the cargo body may be tilted upward at one end of the frame to expedite dumping of the load. The tilting allows gravity to stimulate load removal from the rear end of the cargo body. Alternatively, an ejector panel or moving floor may be used to expedite the removal of the load from the cargo body.
One of the most important agendas of the driver of refuse collection vehicles and dump trucks and other similar vehicles of the foregoing variety is to always carry the maximum load possible. The problem truckers face is that governmental restrictions exist on allowable maximum loads. Load limits have been set to deter damage to roads and bridges caused by excessive loads. Governmental regulations require specific maximum loads for trucks based on the horizontal distance between the front and rear axles of the truck. It is of special interest that this maximum load imposed by government restrictions may be increased with respect to increases in the distance between front and rear axles. It is also of interest that governmental regulations also limit the amount of load that a single axle may carry. The front axles of a truck are generally lightly loaded. By adding a trailing axle, more load can be transferred to these forward axles allowing them to be loaded nearly to their maximum limits.
Trailing axle assemblies have been attached to the rear ends of truck bodies or the rear end of truck frames to increase the legal load capacity of the truck. A trailing axle assembly normally includes an axle at the rear end of the trailing axle assembly and having wheels mounted at either end. There are two extreme positions for the trailing axle. One position is at rest on the ground or road. This effectively increases the overall length from the forward-most axle of the vehicle to the rearward-most axle of the vehicle, i.e., the trailing axle. By distributing the total weight of the load over a longer distance between the front axle and the trailing axle, the allowable load that the dump truck can carry is increased. Therefore, the dump truck can travel on the road and over bridges with an increased load without occasioning damage to roads and bridges.
Regarding dump trucks, the cargo body may be pivoted about the rear end of the frame so that the front end is raised in relation to the rear end of the frame, of which remains in place. The tailgate opens the cargo body of the truck at its rear end. With the tailgate open, gravity acts on the load within the cargo body of the dump truck pulling it towards the ground or into one of many different types of equipment. Preferably, before the tailgate is opened and the cargo body raised, the trailing axle assembly is raised. Raising the trailing axle prevents the load from spreading over part of the trailing axle as it falls out of the cargo body to the ground. Raising the trailing axle also prevents the trailing axle from having to ride over the dumped load which would induce unnecessary stresses on the trailing axle. Raising the trailing axle also allows the load to be dumped into other equipment that must be positioned adjacent to the vehicle.
In order to have the maximum effect for increasing the allowable load, it is desirable for the trailing axle to be a certain distance behind the truck. If the pivot point for the trailing axle is forward of the rear of the truck, the trailing axle when rotated to an upright position would be above the maximum height allowed by government regulations. In this situation, the height must be reduced by some method. There are several disadvantages to prior art trailing axle designs of this variety. In an effort to maintain the legal height of the dump truck and the trailing axle while in the raised position, the prior art has provided hydraulic cylinders and complicated valving and linkage mechanisms to pivot the trailing axle up and over the cargo body of the vehicle. The purpose of the cylinders, valving and linkage is to lower the overall height of the raised trailing axle assembly to conform with government standards. As a consequence, the first disadvantage of the forward pivot feature of the prior art is that the use of cylinders, valving and linkage mechanisms to reduce the height is very costly, complicated and prone to mechanical failure.
A second disadvantage of the prior art forward pivot feature of trailing axle assemblies is the use of lift cylinders for the suspension of the trailing axle. The lift cylinders are designed to absorb shock from bumps and dips in the road as the vehicle is traveling on the road. For example, as the vehicle goes over a bump, the wheels and trailing axle cause the lift cylinders to retract. As the wheels and trailing axle return to the ground, the lift cylinders extend back to their resting position. Thus, the lift cylinders, acting as the suspension system, are required to perform many cycles of movement. This causes excessive and undesired wear on the lift cylinders. The cylinders must also have an accumulator built into them in order to react fast enough to the road bumps and also to return the lift cylinders to their original position after going over a bump, thus dramatically increasing the cost of the lift cylinders.
A further disadvantage of the prior art of the foregoing prior art trailing axle assemblies is that in the stowed position, the trailing axle is over the cargo body which can impede filling the cargo body. Furthermore, the trailing axle of the prior art trailing axle assemblies must be mounted on a toggle to be able to adjust to lateral ground differences without putting undo stress on the trailing axle assembly. This adds considerable expense and complexity to the trailing axle assembly. Yet a further disadvantage of the prior art is that the accumulator must be mounted close to the lift cylinders for them to be fast acting, and a large volume of gas is required in the accumulator so that as the lift cylinders compress the forces and stresses in the trailing axle do not increase too much.
Another method used in the prior art is to have the pivot point for the trailing axle substantially rearward of the rear of the truck and attached to the truck frame. When the trailing axle assembly is attached to the rear end of the truck frame, the height of the trailing axle assembly in the raised position can exceed government regulations. To prevent government regulation violation, one solution has been to shorten the length of the trailing axle assembly. The disadvantage to this practice is that by shortening the length of the trailing axle assembly the maximum increase in the legal load allowances for the truck is not possible. Should the pivot for the trailing axle be moved far enough to the rear of the truck body, the trailing axle when rotated to an upright position would be below the maximum height allowed by government regulations. In this regard, the pivot point becomes an unsafe appendage that does not comply to government regulations and hinders the flow of the load from the cargo body when the front end has been pivoted upwards and the tailgate opened to release the load from the cargo body. This occurs because the trailing axle assembly is connected to the center of the chassis frame between opposite lateral sides of the frame. Therefore, even when the trailing axle assembly is raised, the design still tends to block the release of the dump load from the cargo body.
Another disadvantage of the foregoing prior art apparatus is that the appendages to the trailing axle assemblies also make it difficult or even impossible to dump the load into some types of paving machines. Furthermore, extraordinary measures must sometimes be taken in the design of the tailgate in order to have it not interfere with the trailing axle arm(s) in the raised position. Also, because the trailing axle is mounted directly to the truck frame, stresses in the truck frame increase dramatically. This moment thus added to the truck frame develops additional stresses in the truck frame at the attachment point and elsewhere and can cause failure of the entire trailing axle assembly.
All of the prior art trailing axles have required a "live" power hydraulic system. This has been accomplished on dump trucks, for example, by adding a completely separate hydraulic system to operate the trailing axle, even though the truck already had hydraulic power available from the power take off. This "live" power was deemed necessary because of the complicated valving required to operate the axle and to compensate for cylinder leaks. Many trucks which would use a trailing axle assembly do not normally have live power, so this is an extra expense to add and also adds to the complexity and thus the maintenance of the trailing axle.
The suspension inadequacies of the prior art is another disadvantage of the prior art trailing axle assemblies. This happens because of the inability of the trailing axle assembly to respond smoothly and efficiently to bumps and dips in the road while the wheels of the trailing axle assembly are on the road and the vehicle is traveling down the road. This affects the smoothness and steadiness in the ride of the vehicle while on the road. The inability to respond effectively to road inconsistencies also affects the life of the trailing axle assembly. As the vehicle travels over a dip or bump in the road, forces and stresses are significantly increased, causing bending and undesired changes in the trailing axle assembly.
Another disadvantage of the prior art is the forces that are generated on the trailing axle in the stowed position as the truck goes over bumps and dips. All of the prior art of forward pivot style stow the trailing axle in such a way that the acceleration-deceleration forces (g-forces) of the axle, tires and supporting structure must be taken into the trailing axle arms through some sort of stop in the linkage. As these g-forces can be quite high, the stresses induced in the linkage are also quite high and therefore prone to failure or must be massive and thus expensive.
Yet Another disadvantage of the prior art is that when the lift cylinders are pushing the trailing axle down onto the ground, the lift cylinders put a moment in the arms which puts tension in the top and compression in the bottom. In addition, the lift cylinders put tension in the whole arm as it pushes. Therefore, the two tensions in top of the arm are additive and the tension and compression in the bottom of the arm are subtractive. This requires a much larger and heavier arm to take the additive tensile stresses.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and improved trailing axle assembly.
Another object of the present invention is to provide a trailing axle assembly that is safe and highly efficient.
And another object of the present invention is to provide a trailing axle assembly that is easy to construct.
Still another object of the present invention is to provide a trailing axle assembly that is easy to use.
Yet another object of the instant invention is to provide a trailing axle assembly that is inexpensive.
Yet still another object of the instant invention is to provide a trailing axle assembly that incorporates a spring suspension system to absorb the shock of bumps and dips.
And a further object of the invention is to provide a trailing axle assembly that does not impede the flow of material into the body of a dump truck when the trailing axle assembly is in a stowed configuration.
Still a further object of the immediate invention is to provide a trailing axle assembly that exerts a low degree of stress upon the frame of a vehicle.
Yet a further object of the invention is to provide a trailing axle assembly for maximizing the distance between the front axle of a truck and the rear axle of the truck.
And still a further object of the invention is the provision of maximizing the amount of a load a dump truck may carry.
And yet still a further object of the invention is the provision of providing an actuating element operative for maintaining a trailing axle assembly in an operative position.
Another object of the present invention is the provision of minimizing the amount of stress applied to a trailing axle assembly during operation.